The term urinary calculus/Calculi (e.g., kidney stone(s) and ureteral stone(s)) refers to mass(es) or stone(s), typically solid particle(s), that form in the human body and is located in the kidney and/or the ureter. They can exhibit a variety of chemical compositions including calcium oxalate, calcium phosphate, uric acid, cystine, and struvite.
Stone disease (e.g., kidney stones and ureteral stones) is a relatively common urological disorder. The presence of calculus in the body can manifest itself in a variety of ways and can produce a number of medical ailments. For example, the presence of calculus in the renal pelvis and/or the renal calix (i.e., the lumen of the kidney) can cause blood in the urine, urinary obstruction, infection, and various degrees of pain ranging from vague frank pain to much more severe pain not capable of being relieved through general pain medication. The presence of stones or calculi in the ureter can result in relatively severe side and back pain, pain below the ribs, and pain that sometimes spreads to the lower abdomen and groin, as well as pain during urination and hematuria.
Fortunately, many calculi or stones pass out of the body without requiring any specific medical intervention. In those situations where the calculus does not naturally pass out of the body, a medical procedure may be required. Known medical procedures typically fall into three categories.
In the past, three main treatments have been used to address calculus or kidney stones. These include shock wave lithotripsy (ESWL), transurethral lithotripsy or ureteroscopy (URS), and percutaneous nephrouretero lithotripsy (PCNL) which is sometimes also referred to as percutaneous nephrolithotomy (PCN).
Shock wave lithotripsy is performed as an extracorporeal treatment. This treatment utilizes a machine called a lithotripter that operates by directing ultrasonic or shock waves from outside the body, through the skin and tissue, and at the calculi or stones. Repeated shock waves apply stress to the stones, eventually breaking the individual stones into smaller pieces which can more easily pass through the urinary tract in urine. One benefit associated with shock wave lithotripsy is that it is a rather simple procedure. But it has been found that there is a relatively high rate of kidney stone recurrence following shock wave lithotripsy.
Transurethral lithotripsy or ureteroscopy represents one such alternative form of treatment. This treatment involves the use of small fiber optic instrument (endoscope) called an ureteroscope which allows access to the calculus in the ureter or kidney. The ureteroscope can be a rigid ureteroscope or more commonly, a flexible ureteroscope. The ureteroscope allows the medical professional to visualize the stone as the ureteroscope moves along the ureter or enters the kidney by way of the bladder and the urethra. Once the calculus is visualized, a basket-like device is used to grasp smaller stones and remove them. If the calculus is excessively large to remove as a single piece, it can be broken into smaller pieces by using laser energy.
The third form of treatment is percutaneous nephrolithotomy. This procedure is often used with relatively larger calculus that cannot be effectively treated with either ESWL or URS. Percutaneous nephrolithotomy involves nephrostomy; making an incision at the appropriate location, needling by paracentesis needle, positioning a guide wire through the paracentesis needle's lumen into the kidney under radiographic guidance, and then expanding perforated site. A nephroscope is then moved into the kidney via nephrostomy to visualize the calculus. Fragmentation of the calculus can be performed using an ultrasonic probe or laser.
Though these procedures have been commonly used, they are susceptible of certain short comings. For example, the ESWL procedure results in a relative large number of small calculi or small stones, while other procedures require a relatively narrow and long access route or are difficult to implement due to the inability to accurately capture the stones. In addition to, many crush pieces should be removed one by one in URS and PCNL procedure. The procedure time can also be excessively long, and can result in a relatively low “stone free rate.” The recurrence rate can also be unacceptably high. And the potential patient complications (e.g., ischemia of the ureter, obstruction of ureter, back-flow and/or high-stress to the renal pelvis, infection of the urinary tract, and other possible injury) can be undesirably high.
Instances also arise, when performing procedures to gain access to calculus, as well as other procedures not specifically involving calculus, where it is desirable or necessary to advance a device into a narrow region in the living body or along an extremely curved path in the living body. The operational procedure can be performed using endoscope (ureteroscope), where the device is positioned in the instrument channel of the endoscope. The device and the endoscope tend to be rather rigid and thus not well suited to being advanced into a narrow region in the living body or moved along an extremely curved path in the living body.